In recent technologies of blood transfusion, blood component transfusion is performed, in which components of blood (whole blood) obtained from blood donation and the like are separated, and only a component necessary for a patient is supplied. The blood component transfusion enables reduction of burdens or side effects on a patient's circulatory system and efficient use of the donated blood.
In the separation of the blood components, a centrifuge machine separates blood into a supernatant (platelet poor plasma) fraction, a heavy precipitation (concentrated red blood cell) fraction, and buffy coat formed therebetween. These components are transferred to predetermined preservation bags, using a blood bag system attachable to the centrifuge machine. The blood bag system disclosed in the specification of U.S. Pat. No. 6,910,998 includes a blood bag in which blood is preserved, a tube with one end connected to the blood bag, and a preservation bag to which the other end of the tube is connected. For example, a centrifugally separated supernatant liquid (supernatant fraction) is transferred to the preservation bag from the blood bag through the tube.
By the way, in the blood bag system attached to the centrifuge machine as described above, the blood is spread from the blood bag to the tube extending to the preservation bag, and a slight amount of the blood is transferred to the tube extending to the preservation bag, when the blood is preserved in the blood bag by blood donation or the like (or before centrifugal separation is performed). Such transferred blood does not especially influence on quality of a blood component even if the blood is mixed in a supernatant liquid circulated in the tube. However, the color of whole blood (red blood cells) stands out from the supernatant liquid. Therefore, even if a very small amount of blood is mixed, a user and the like may feel the quality of the blood product has low quality.